1. Field of the Invention
Aspects of the present invention relate a secondary battery that can improve an attachment between a molded resin part and a cap assembly.
2. Description of the Related Art
Generally, a secondary battery is a battery capable of being charged and discharged several times. Secondary batteries have been used for high-tech electronics, such as, cellular phones, notebook computers, camcorders, and the like.
An operating voltage of a lithium secondary battery is 3.6 volts, which is three times larger than that of a nickel-cadmium (Ni/Cd) battery or a nickel-hydrogen battery (Ni/H2), which are also used to power electronic equipment. Thus, the high energy density of a lithium secondary battery has led to its widespread adoption.
A lithium secondary battery generally uses a lithium-based oxide as a cathode active material and a carbon material as an anode active material. Lithium secondary batteries have been manufactured in various shapes, such as, a cylindrical shape, a polygonal shape, a pouch shape, and others. A polygon-shaped secondary battery comprises a bare cell, a protection circuit board, and a molded resin part.
The bare cell includes: an electrode assembly, a can to receive the electrode assembly; and a cap assembly attached to an opening of the can. The cap assembly includes: a cap plate attached to the opening of the can; an electrode terminal extending through a through-hole in the cap plate; a gasket placed on the outer surface of the electrode terminal, to insulate the cap plate; an insulation plate positioned under the cap plate; and a terminal plate positioned under the insulation plate, so as to allow electricity flow through the electrode terminal.
The protection circuit board includes a protection circuit, which protects the battery from getting overcharged and over-discharged during charging/discharging operations. The protection circuit board can be electrically connected with electrodes of the bare cell, through a lead plate.
The molded resin part is formed by filling a hot-melt resin into a space between the cap plate and the protection circuit board and then allowing the resin to harden. The molded resin part prevents battery components from moving between the cap plate and the protection circuit board.
The molded resin part may be attached to the lead plate placed between the cap plate and the protection circuit board. However, since the cap plate becomes narrower as the size of the battery is reduced, the lead plate is welded to an upper surface of the cap plate in one line. A detachment of the molded resin part from the cap assembly, as a result of external forces, such as, twisting or bending of the battery, cannot be prevented by only the lead plate.
Conventionally, a holder has been additionally positioned on the upper surface of the cap plate, in order to strengthen the attachment between the cap plate and the molded resin part. The holder prevents the relative motion of the molded resin part and the cap plate, or prevents the molded resin part from being separated from the cap plate.
However, since such a holder is positioned on the upper surface of the cap plate, additional processes are required for manufacturing such a secondary battery, thereby increasing the associated manufacturing costs and time. In addition, an additional space is required for positioning the holder on the upper surface of the cap plate, thereby causing a limitation in the space utilization in the battery. Further, total height of the battery is increased, thereby causing a decrease in battery capacity, or an increase in the size of the battery.